The ad calls for Canadians to sign a petition opposing the bill. However, the ad, which features Mulcair, doesn't state how the bill will give the Conservatives an unfair advantage in the 2015 federal election.

The NDP have previously stated that the bill, which eliminates the practice of vouching, will prevent tens of thousands of people from casting ballots.

A voter without proper identification on election day can vote if another citizen with ID "vouches" for them.

The Conservatives say that vouching is too susceptible to voter fraud.

Also on Thursday, a who's who of the Canadian left, including novelist Margaret Atwood and environmentalist David Suzuki, signed a letter to Prime Minister Harper denouncing the bill, which they also said will "stack the deck" in favour of the governing party.